It is the conventional practice in the manufacture of oil pipes in automotive engines to braze end-fittings onto the lengths of pipe. The end-fitting includes a forward-pointing nose, backed by an enlarged portion. Conventionally, behind the enlarged portion of the end-fitting is a threaded nut, which engages a complementarily-threaded hole in the engine block or other component into which the pipe is fitted.
An automotive engine is a demanding environment, in that the inevitable vibrations, temperature extremes, etc, can tend to make a threaded fastener work loose. And, from a service standpoint, oil-pipes are expected never to work loose throughout the whole life of the vehicle. If an end-fitting works loose, and the lubricating oil leaks out, the engine may be destroyed.
Bearing in mind these factors, it is the common practice for the designer to "over-engineer" the end-fittings on oil-pipes. Penny-pinching on oil-pipe end-fittings has been seen as imprudent. As a result, oil-pipe end-fittings have been produced more expensively than is now seen to be necessary.
The designer has also had to bear in mind that the installation of, for example, an oil-pipe into an engine-block, on the engine-building production line, requires careful attention, and the exercise of some degree of skill, on the part of the installation operative, and such attention and skill cannot always be totally relied upon. Even though the end-fitting may be highly robust and effective in itself, if the end-fitting is not properly installed, oil may leak out.
Designers often prefer to consider, for such applications as automotive oil-pipes, connectors which have, not a screw-thread type of connection, but a push-in-and-snap type of connection. When a push-in-and-snap connection is properly engineered, the connection can be just as reliably secure against leakage as a screw-thread type of connection, but can be more economical to manufacture, and require less skill and attention from the assembly operative.
The invention is aimed at providing a highly reliable end-fitting for a pipe, wherein the end-fitting, having been properly installed, is the equal of conventional end-fittings from the standpoint of resistance to leakage during service; wherein the end-fitting is almost impossible to be assembled improperly on the production line; and wherein the end-fitting is highly economical to produce.
For a robust and secure attachment of the end fitting, the designer requires that the diameter of the enlarged portion be considerably larger than the nominal diameter of the pipe. As mentioned, the conventional practice has been to braze the end-fittings onto the pipe. A brazed-on end-fitting may be made as a lathe-turned component in brass, which is brazed to the (steel) pipe.
However, it is now becoming standard practice to swage the end of the pipe itself to form the end-fitting. One of the problems when swaging the end-fitting is to provide enough local enlargement of the diameter of the pipe as to provide a good abutment upon which a pipe-nut can engage, and be tightened down, or against which a snap-clip can engage.
If the designer calls for too much enlargement by swaging, the pipe material may start to pucker, or otherwise distort, which might lead to a faulty seating of the end-fitting, and a consequent leakage of oil at the joint.